1. Field of The Invention
The present invention relates to an apparatus for introducing a stream containing a high oxygen concentration into a wet oxidation reactor used for oxidizing combustible materials in liquid water.
2. Description of the Prior Art
In wet oxidation systems using pure oxygen or oxygen concentrations in excess of 25 percent, safe introduction of the oxygen into the wet oxidation reactor is of utmost importance. The design of the oxygen inlet pipe is critical because the oxygen partial pressure is highest in the inlet pipe, as compared to the partial pressure in any other location in the reactor. Introduction of water (hereinafter called "purge water") together with the oxygen is suggested in order to maintain a continuous positive flow in the oxygen line at all times. Backflow of combustibles from the wet oxidation reactor into the oxygen line is thus prevented. Another important function of the purge line is to provide a heat sink for any hot spots which may be generated due to oxidation of combustibles within or at the end of the oxygen line.
The stream of oxygen and purge water is usually introduced at the bottom of the wet oxidation reactor through a pipe which extends from the wall of the reactor to a point of discharge so as to facilitate good gas dispersion in the reactor. When the wet oxidation reactor is a vertical bubble column, the point of oxygen discharge inside the reactor is preferably near the centerline of the reactor vessel. The temperature of the gas-liquid mixture surrounding the end of the oxygen injection nozzle is often very nearly that of the maximum reactor temperature.
The operating temperature of the wet oxidation system may vary from 300.degree.-650.degree. F., depending upon the particular objective of the process. When operating at high temperatures, for example 620.degree. F., the oxygen pipe inside the reactor, from the reactor wall to the point of discharge, may be heated sufficiently to produce a significant temperature rise in the stream of oxygen and purge water. Some or all of the purge water may evaporate if its temperature is sufficiently increased.
The rate of purge water addition to the stream of oxygen or oxygen-enriched air can vary for 0.01 to 10 pounds water per pound of oxygen, depending upon the process. Since purge water directly contacts the oxygen at elevated pressure, i.e., 300-3500 psig, the water must be free of contaminants which will oxidize or form scale on the pipe surfaces. Potable, deionized, or distilled water may be suitable as purge water. Use of deionized or distilled water will incur substantial additional costs. Use of a high rate of purge water is generally undesirable because dilution of the wet oxidation fuel results in energy losses, analogous to adding water to the fuel which is combusted in a boiler. Use of potable water at the lowest purge water rate is most desirable to produce a cost effective system.
In a wet oxidation system operating at high temperatures, i.e., 620.degree. F., and a low purge water rate of 0.1 pound water per pound oxygen, the heat transfer from the reactor contents into the stream of purge water and oxygen or oxygen-enriched air may be sufficient to cause a significant temperature rise in the stream before it discharges into the reactor. This temperature rise may result in:
(a) elimination of positive liquid water flow in the oxygen nozzle pipe caused by nearly complete evaporation of purge water in the nozzle pipe, and
(b) scaling and deposition of salts in the oxygen nozzle pipe, with its eventual plugging.
Increasing the reactor pressure to reduce evaporation requires a more expensive thicker-walled reactor, and in many cases is precluded by the system objectives.
The present invention discloses a design for an oxygen inlet nozzle for a wet oxidation system which eliminates the above problems and enables the use of potable water at low flow rates as purge water for safe introduction of pure oxygen or oxygen-enriched air into the wet oxidation reactor.